Cigarette lighter sockets are typically provided in cars these days and when they collaborate with cigarette lighters, drivers can use the cigarette lighter sockets to light up cigarettes. However, due to the environmentally-friendly trend and personal health concerns, the function of lighting up cigarettes is gradually replaced by the function of supplying power to electronic products because a driver may need to use various electronic products, such as satellite navigation, an event data recorder and a cellphone, while driving a car.
Due to the demand in supplying power to various electronic products from the cigarette lighter socket, a variety of products are developed, e.g. a cigarette lighter socket with one-to-many expansion function and a cup-shaped power socket in a drink holder for a car. No matter what kind of the product is, a cigarette lighter plug needs to be inserted into the above-mentioned cigarette lighter socket for application. However, when driving a car on an uneven road, the cigarette lighter plug may be jolted to be detached from the cigarette lighter socket, and in solution, there are various cigarette lighter sockets developed to prevent such condition.
One kind of design for preventing detachment of the cigarette lighter plug is to make a conductive flexible plate of the cigarette lighter plug protrude more outwardly. Therefore, after the cigarette lighter plug is inserted into the socket, it fully relies on the conductive flexible plate to prevent the cigarette lighter plug from loosing. In such design, a protruding length of the conductive flexible plate is very important. If too loose, the design is not working; if too tight, the user could not pull out the plug from the socket. Moreover, in the too tight circumstance, even though the plug is pulled out, the conductive flexible plate and the wire may be left in the socket during the pulling-out process.
Please refer to FIG. 1 which shows another cigarette lighter socket A for preventing detachment of the cigarette lighter plug. An external thread A1 with a conical degree is formed on an end of the cigarette lighter socket A, where the cigarette lighter plug B is inserted. After the external thread A1 is formed, a plurality of slits A2 are formed on an outer circumferential surface. The end having the slits also includes a plurality of lateral edges A3 disposed independently. Furthermore, a hollow circular cover A5 having an internal thread A51 corresponding to the external thread A1 can be threadedly fastened to the end. This configuration prevents detachment of the cigarette lighter plug B as detailed below. Upon threadedly fastening the external thread A1 to the internal thread A51, due to the conical degree of the external thread A1, the hollow circular cover A5 exerts a compress force to the lateral edges A3, and the lateral edges A3 contracts radially inwardly by means of the slits A2, and thus the cigarette lighter plug B can be stably inserted into the cigarette lighter socket A.
The conventional cigarette lighter socket mentioned above has the following defects in need of improvement.
A manufacturing process of the cigarette lighter socket A is troublesome. After the external thread A1 is formed, a plurality of slits A2 also have to be formed on the circumferential surface, and consequently, a production cost increases. However, if it is desired to use an integral molding method, it is very complicated to design a mold for this method. Due to the fact that the socket A in the same mold includes a smooth and also externally threaded outer circumferential surface, a production yield can be affected, and the production efficiency is also reduced.
Furthermore, the slits A2 may be exposed after the hollow circular cover A5 is threadedly fastened, so it is very likely that accidentally spilled water near the socket A will enter the socket A from the exposed slits A2, and thus a short circuit may occur and cause serious damage.
Finally, since the hollow circular cover A5 has a knurl structure on its outer surface and has the internal thread A51 on its inner surface, the hollow circular cover A5 needs to have a certain thickness (in a radial direction). The external thread A1 of the socket A is formed on the outer circumferential surface of the socket A. Therefore, after the hollow circular cover A5 is threadedly fastened, the thickness obviously protrudes from the outer circumferential surface of the socket A, and as a result, the whole appearance is not attractive. If choosing to make the socket A thicker in order to match the thickness of the hollow circular cover A5, the manufacturing process will be even more troublesome, and the production cost will also increase.